How popular is Tahnya?

Tahnya is an uncommonly occurring first name for females. Tahnya is an equally uncommon surname for all people. (2000 U.S. Census)

Which version is better?

with its source form and related girl names. Prominent alternative forms of Tahnya (outside Top 2000) ranked in the Top 2000 are Taina, Tana, Tania(#1481 from current records), Tanja, Tanya(#1933), Tawnya and Tonya. Usage of these relations of Tahnya was well-received among parents in the 1970s (median #749) and is now significantly diminished (#1916, 99% less usage). (2015 Birth Statistics)